Method of retransmitting data in a wireless communication system and apparatus for implementing the same

ABSTRACT

A method of transmitting data in a wireless communication system is disclosed. More specifically, the method includes receiving a first group index and a second group index, wherein the first group index represents indices of a group having channel power below a specified threshold value and the second index group index represents indices of a group having channel power greater than or equal to the specified threshold value, and transmitting the data after swapping mapping locations of the first group index and the second group index.

TECHNICAL FIELD

The present invention relates to a method of transmitting data, and moreparticularly, to a method of transmitting data is a wirelesscommunication system and an apparatus for implementing the same.

BACKGROUND ART

With fast growing use and popularity of multimedia and communicationservices, demand for faster and more reliable wireless communicationservices is also increasing at a fast rate. In order to accommodate suchchanging demands, the capacity of the wireless communication systemneeds to improve as well. To this end, the capacity can be improved bybetter utilizing and increasing the efficiency of the existing limitedwireless resources.

As an example of improving the use of the existing limited wirelessresources, a transmitter and a receiver can respectively be equippedwith more than one antenna. With more than one antenna, diversity gaincan be achieved with respect to spatial domain, and transmit diversitycan be increased by transmitting data via each antenna in parallel.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is directed to a method oftransmitting data is a wireless communication system and an apparatusfor implementing the same that substantially obviates one or moreproblems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a method oftransmitting data is a wireless communication system.

Another object of the present invention is to provide a method ofretransmitting data in a wireless communication system.

A further object of the present invention is to provide an apparatus forretransmitting data in a wireless communication system.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, [amethod of transmitting data is a wireless communication system includesreceiving a first group index and a second group index, wherein thefirst group index represents indices of a group having channel powerbelow a specified threshold value and the second index group indexrepresents indices of a group having channel power greater than or equalto the specified threshold value, and transmitting the data afterswapping mapping locations of the first group index and the second groupindex.

In another aspect of the present invention, a method of retransmittingdata in a wireless communication system includes measuring power valuesof a receiving channel in terms of subcarriers or subcarrier groups pereach antenna, generating feedback information based on the measuredpower values, receiving the feedback information regarding channelinformation in terms of the subcarriers or the subcarrier groups foreach transmit antenna, allocating the data to the subcarriers or thesubcarrier groups, which were mapped to the subcarriers or thesubcarriers groups having relative poor channel condition, to thesubcarriers or the subcarrier groups having relative good channelcondition, and retransmitting the data on the allocated subcarriers orthe subcarrier groups via a plurality of antennas.

In a further aspect of the present invention, an apparatus forretransmitting data in a wireless communication system includes at leastone encoder configured to attach error correction bits, at least onehybrid automatic request function module configured to perform at leastone of retransmission and rate matching, at least one mapper configuredto convert parallel signals into symbols, a resource allocation moduleconfigured to allocate the data to subcarriers, and an allocationcontroller configured to receive feedback information from a receiver,wherein the resource allocation module controls transmission by changingthe subcarrier index, having large fading during initial transmission,with the subcarrier index having good channel condition.

Yet, in another aspect of the present invention, an apparatus forretransmitting data in a wireless communication system includes at leastone fast Fourier transform (FFT) module configured to process thesymbols transmitted from a transmitter, at least one demapper configuredto convert the symbols into signals, an index selection moduleconfigured to measure receiving channel power of each subcarrier or eachsubcarrier group corresponding to each transmit antenna, and a storageunit configured to store at least one subcarrier index or at least onesubcarrier group index, wherein the measured channel power is comparedto a predetermined threshold value and the subcarrier index or thesubcarrier group index whose value I is greater than or equal to thepredetermined threshold value is stored in the storage unit.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIG. 1 is a diagram illustrating a transmitter and a receiver using asingle codeword (SCW) scheme in an orthogonal frequency divisionmultiplexing (OFDM) multi-antenna communication system;

FIG. 2 is a diagram illustrating a transmitter and a receiver using amultiple codeword (MCW) scheme in an OFDM multi-antenna communicationsystem;

FIG. 3 illustrates a communication system having two (2) transmitantennas in which the resource allocation module allocates a firsttransmission of data and a second transmission of data via a sameantenna;

FIG. 4 illustrates a communication system having two (2) transmitantennas in which the resource allocation module allocates a firsttransmission of data and a second transmission of data via differentantennas;

FIG. 5 is an exemplary diagram illustrating measuring the power of areceiving channel at a receiver and generating feedback information tocontrol data retransmission;

FIG. 6 is an exemplary diagram illustrating locations for allocation ofdata during retransmission according to an embodiment of the presentinvention;

FIG. 7 is an exemplary diagram illustrating locations for allocation ofdata during retransmission according to another embodiment of thepresent invention;

FIG. 8 is an exemplary diagram illustrating generating feedbackinformation based on a specified number of groups of subcarriers forretransmission;

FIG. 9 is an exemplary structural diagram illustrating a transmittingend and a receiving end using a SCW scheme;

FIG. 10 is an exemplary structural diagram illustrating a transmittingend and a receiving end using a MCW scheme;

FIG. 11 is an exemplary diagram illustrating comparison ofretransmission method according to the embodiment of the presentinvention to the conventional retransmission method; and

FIG. 12 illustrates retransmission of data according to at least one ofthe embodiments of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a diagram illustrating a transmitter and a receiver using asingle codeword (SCW) scheme in an orthogonal frequency divisionmultiplexing (OFDM) multi-antenna communication system. FIG. 2 is adiagram illustrating a transmitter and a receiver using a multiplecodeword (MCW) scheme in an OFDM multi-antenna communication system.

Referring to FIG. 1 and FIG. 2, the transmitter 100 of the OFDMmulti-antenna communication system comprises an encoder 101, a modulehaving hybrid automatic request (HARQ) function 102 (hereinafterreferred to as “HARQ module”), a channel interleaver 103, aserial-to-parallel (S/P) converter 104, a mapper 105, a resourceallocation module 106, and an inverse fast Fourier transform (IFFT)module 107.

More specifically, the encoder 101 is used to reduce noise and effectfrom the channel caused by a coding method in which extra bits areattached or inserted to the data bits. The HARQ module 102 is used toperform retransmission and/or rate-matching. Moreover, the channelinterleaver 103 is used to shuffle the data bits, which includes thecyclic redundancy check (CRC), so as to spread the burst error in achannel. The S/P converter 104 is used to convert serially inputtedsignal into parallel signal.

Furthermore, the mapper 105 is used to convert the parallel signal (orbits) into symbols. The resource allocation module 106 is used toallocate (or map) the symbols to subcarriers, and the IFFT module 107 isused to modulate the allocated symbols to OFDM symbols and send themodulated OFDM symbols to channel 300.

The transmitter 100 shown in FIG. 1 uses the SCW scheme. Here, because asingle codeword is used, the transmitter 100 includes only one of eachencoder 101, HARQ module 102, and channel interleaver 103. In case ofthe transmitter 100 of FIG. 2, there are two (2) encoders 101, two (2)HARQ modules 102, and two (2) channel interleavers 103, based on two (2)codewords used.

With respect to the receiver 200 of FIG. 1 and FIG. 2, the receiver 200includes a fast Fourier transform (FFT) module 201, a resourcede-allocation module 202, a demapper 203, a parallel-to-serial (P/S)converter 204, a channel de-interleaver 205, a module having inverseHARQ function (hereinafter referred to as “HARQ-inverse module”) 206,and a decoder 207. In operation, the receiver 200 receives the signalfrom the transmitter 100 and processes the signal in reverse order fromthose of the transmitter.

More specifically, the FFT module 201 and the resource de-allocationmodule 202 processes the data signals (or symbols) passed through thechannel 300. Thereafter, the processed symbols are converted into bitsby the demapper 203 and further processed through the P/S converter 204and the de-interleaver 205. Then, the processed data bits arerate-matched for decoding purposes at the HARQ-inverse module 206 andprocessed through the decoder 207 from which the data is decoded.

After the data (or data packet) is decoded, possible error can bedetected via the error detection code (e.g., CRC bits). If error isdiscovered with the decoded data packet, the receiver 200 sends anegative acknowledgement (NACK) signal to the transmitter 100.Conversely, if no error is discovered with the decoded data packet, thereceiver 200 sends a positive acknowledgement (ACK) signal to thetransmitter 100.

If the transmitter 100 receives the ACK signal, then no action is takenwith respect to the previously transmitted data packet. However, if thetransmitter 100 receives the NACK signal, then the transmitter 100retransmits the data packet. The retransmission can take place accordingto the transmission schedule determined by a scheduler.

With respect to data (or data packet) retransmission, FIG. 3 and FIG. 4describe in more detail the processes associated with retransmission inview of the resource allocation module 106.

FIG. 3 is a diagram illustrating retransmitting data from the resourceallocation module by fixing the assigned transmit antennas. FIG. 4 is adiagram illustrating retransmitting data from the resource allocationmodule by changing the assigned transmit antennas.

More specifically, FIG. 3 illustrates a communication system (e.g.,multi-input, multi-output (MIMO) system) having two (2) transmitantennas in which the resource allocation module allocates a firsttransmission of data and a second transmission of data via a sameantenna. Alternatively, FIG. 4 illustrates a communication system havingtwo (2) transmit antennas in which the resource allocation moduleallocates a first transmission of data and a second transmission of datavia different antennas. Here, the transmission of data via differentantennas can be accomplished by antenna permutation.

In an OFDM structure, each subcarrier can be transmitted in anenvironment having favorable channel condition or in an environmenthaving large fading. Some of the subcarriers (or subcarrier bandwidth)experiencing large fading are the subcarriers which can bring down theentire system capability. In order to compensate for such a phenomenon,a channel coding scheme can be used. However, if the degree of fading issevere, then the channel coding scheme may not be enough.

As such, if an index of the antennas is shuffled for retransmission ofdata as shown in FIG. 4, a diversity gain can be achieved compared tothe retransmission method as shown in FIG. 3. That is, if the firsttransmission of data experiences poor channel condition but the secondtransmission of data experiences good channel condition, then the poorchannel condition is partially compensated by the good channelcondition. In other words, deterioration of the communication systemperformance caused by large fading can be prevented and/or alleviated.

Despite the potential positive outcome, if the antenna index isarbitrarily shuffled, it is possible that a channel having poorcondition (e.g., first transmission) may be changed to another channelhaving a poor channel condition (e.g., second transmission).Alternatively, the converse can be true. That is, the first transmissionhaving a good channel condition may be changed with the secondtransmission also having a good channel condition. Such occurrencesnegate diversity gain.

Furthermore, it is possible that the transmitted data on each antennavia a specific subcarrier (or subcarrier bandwidth) can experience avery good or a very bad channel condition, it may be necessary for dataallocation for retransmission to consider various channel environments.

FIG. 5 is an exemplary diagram illustrating measuring the power of areceiving channel at a receiver and generating feedback information tocontrol data retransmission. More specifically, the receiver can measurethe power of the receiving channel in terms of subcarriers per eachantenna, and using the measured values, the feedback information can begenerated.

Referring to FIG. 5, the receiver can measure the power of the channelper each subcarrier for each of the two (2) transmit antennas (e.g., Tx1and Tx2). The measured power values can then be compared with adetermined threshold value to determine index of the subcarriersexperiencing large fading. In FIG. 5, the subcarriers or subcarrierbandwidth experiencing large fading is indicated by S_(k) and S_(j).

Here, the threshold value can be configured based on the severity ordegree of fading. If the threshold value is configured to be a relativehigh value, the performance improvement may increase but the subcarrierbandwidth with large fading becomes smaller in relation. Therefore, themore feedback information needs to be transmitted. As such, thethreshold value can be configured based on the degree of compensationfor fading channel required by the system and the amount of feedbackinformation.

In order to retransmit the data, transmitted via the subcarriers havinglarge fading, via channels having good channel quality, the index ofsubcarrier bandwidth having channel power of the subcarrier bandwidthfor each transmit antenna greater than the threshold value. Asillustrated in FIG. 5, if there is a plurality of indices of thesubcarrier bandwidth having channel power greater than the thresholdvalue, the indices can be selected based on the largest channel power,and the number of selected indices can correspond to the number ofsubcarrier indices determined to experience large fading. Moreover, inFIG. 5, S_(n) and S_(i) denote subcarrier indices having good channelconditions.

According to an embodiment of the present invention, the feedbackinformation can include the subcarrier index (S_(k), S_(j)) having apoor receiving channel condition and the subcarrier index (S_(n), S_(i))having a good receiving channel condition. After receiving the feedbackinformation, the transmitter can map (or allocate) the data transmittedvia the subcarriers of S_(k), S_(j) to the subcarriers S_(n), S_(i) forretransmission of the data. With this, the system can experience lessdeterioration of performance.

FIG. 6 is an exemplary diagram illustrating locations for allocation ofdata during retransmission according to an embodiment of the presentinvention. FIG. 7 is an exemplary diagram illustrating locations forallocation of data during retransmission according to another embodimentof the present invention.

In detail, FIG. 6 is similar to FIG. 3 in that the transmit antennas arefixed (unchanged) for retransmission. Furthermore, in FIG. 6, thereceiving channel information is received in terms of subcarriers foreach transmit antenna. Thereafter, the data which were mapped tosubcarriers having large fading (e.g., relative poor channel condition)is mapped (or reallocated) to the subcarriers having good channelcondition. These subsequently mapped (or reallocated) data are thenretransmitted on the subcarriers having good channel condition. Here,‘D’ denotes data transmitted via the first antenna (Tx1) during initialtransmission, ‘P’ denotes data transmitted via the second antenna (Tx2)during initial transmission, ‘F’ denotes subcarrier(s) having largefading based on the feedback information, and ‘T’ denotes subcarrier(s)having a good channel condition.

As illustrated in FIG. 6, with respect to mapping subcarriers, thelocations of (T, F) are changed during retransmission. Therefore, if theinitial transmission was affected by large channel fading, theretransmission can compensate for the poor channel condition by changingthe locations of the subcarriers during retransmission.

FIG. 7 is similar to FIG. 4 in that the transmit antennas can change forretransmission. Furthermore, in FIG. 7, the receiving channelinformation is received in terms of subcarriers of each transmitantenna. Thereafter, the data mapped to subcarriers having large fadingis retransmitted after being mapped (or reallocated) to subcarriershaving good channel condition. The symbols (e.g., D, P, F, and T) arethe same as those from FIG. 6.

The resource allocation module of the transmitter can change thelocations of (T, F) with respect to subcarrier mapping during dataretransmission. Here, the subcarrier index can be the subcarrier indexof a same transmit antenna or can be the subcarrier index of a differenttransmit antenna.

According to the mapping schemes of FIGS. 6 and 7, as discussed, thetransmission of data can be compensated during retransmission since thedata transmitted via subcarriers with large channel fading isretransmitted via subcarriers having a good channel condition. As aresult, the system performance is as a whole can improve.

Referring to FIG. 5-7, the receiving channel power of each subcarrier ofeach antenna can be measured and based on this measurement, the datamapping index can be changed during retransmission. Here, the channelpower measurement and/or data mapping does not have to be limited tosubcarriers and can be applied to a group of subcarriers or a pluralityof subcarriers.

FIG. 8 is an exemplary diagram illustrating generating feedbackinformation based on a specified number of groups of subcarriers forretransmission. In FIG. 8, a group of subcarriers (hereinafter referredto as a “subcarrier group or subcarrier block (SB)”) can be the basisfor determining the channel power and changing the data allocationlocation.

As discussed, the method of generating the feedback information usingthe determined receiving channel power and changing the locations of thedata (e.g., allocation re-mapping) during retransmission can also beapplied to the SB. In other words, the SB can be also used in a samemanner as the subcarriers. For example, each symbol of the index (T, F)can represent group(s) of subcarriers.

As applied to the SB, the channel power of the SB can be the averagepower of the subcarriers in each group. Furthermore, an additionalthreshold value can be applied based on the degree (or severity) offading so as to provide weight to specific subcarrier when determiningthe average of the channel power within the SB. Even though the amountof calculation may increase, the average channel power can be morerealistic.

Referring to FIG. 8, SB_(k), SB_(i) can be used to indicated an index ofthe SB (or SB index) which experiences large fading, and SB_(n), SB_(j)can be used to indicate the SB index having a good channel condition.These indices can be stored and transmitted as feedback information tothe transmitter. At the transmitter, during retransmission, the indices(SB_(k), SB_(i)), (SB_(n), SB_(j)) can be changed and the data can beremapped using the changed indices.

If the SB is applied as is the case in FIG. 8, improvement to the systemperformance may be relatively smaller than the improvement of FIG. 5.However, the amount of calculation and/or amount of feedback informationcan be reduced.

In other words, if the feedback information is generated after measuringthe received channel power in terms of subcarriers, as illustrated inFIG. 5, the amount of data (or indices) stored as the feedbackinformation equals the number of the transmit antennas and the number ofthe subcarriers of each transmit antenna. Here, the stored data (orindices) can be stored in form of an array. However, it is not necessaryto store all of the data. Instead, the amount of data (or a number ofindices) that corresponds to the indices of the subcarriers havingchannel power below a certain threshold can be stored.

As illustrated in FIG. 8, if the feedback information is generated aftermeasuring the received channel power in terms of a specified number ofsubcarrier groups or SB, the amount of data (or a number of availablearrays) may be reduced according to the number of subcarriers in thesubcarrier groups. At the same time, the number of indices experiencinglarge fading, as a result of having channel power below a predeterminedthreshold, can also be reduced. Here, however, the level of improvementof system performance may not be as great compared to when the channelcondition of each subcarrier was contemplated. In particular, in arelatively unstable channel condition environment, differences inchannel power of each subcarrier may be large, and as a result, it maybe difficult to group the subcarriers (or difficult to apply the SB).However, in an environment where the differences in channel power aresmall, it may unnecessary to group the subcarriers (or apply SB).

In an embodiment of the present invention, the level (or degree) ofcorrelation between the subcarriers were measured, and based on thevalue of correlation, further determinations were made. For example, ifthe correlation value is large, determination is made that there issmall channel variation per each subcarrier. Based on thisdetermination, the feedback information is generated retransmitted interms of SB (or subcarrier group), as shown in FIG. 8. Alternatively, ifthe correlation value is small, determination is made that there islarge channel variation per each subcarrier, and based on thisdetermination, the feedback information is generated and transmitted interms of subcarriers, as shown in FIG. 5.

Further, the amount of change in channel power according to user's (orterminal's) mobility can be expressed as shown in Equation 1. Theembodiment of the present invention applies to various situations withrespect to the user's or terminal's level of mobility. That is, theuser's mobility can refer to the speed at which the user is movingand/or the amount of movement. The embodiments of above can be applied,but not limited to, situations where the user's mobility is small ormoderate (i.e., not much change in channel condition duringretransmission). As such, it may be necessary to compensate for thiswhen the user's mobility is high.

|Ξ_(n)|²=(1−|ρ|²)σ_(h) ²  [Equation 1]

Here, |Ξ_(n)|² denotes the amount of change in channel power accordingto the user's mobility, σ_(h) ² denotes average energy of the channel,and ρ denotes a variable acquired by using Bessel function with respectto Doppler frequency and time delay in time-varying channel environment.ρ p can be further expressed as shown in Equation 2.

ρ=J ₀(2πf _(d)τ_(d))  [Equation 2]

Here, J₀ (•) denotes Bessel function, f_(d) denotes Doppler frequency,and τ_(d) denotes time delay. According to Equation 2, ρ is inverselyproportional to user's mobility in that ρ decreases with increase in theuser's mobility, and conversely, ρ increases with decrease in user'smobility. For example, ρ=1 denotes complete (or perfect) channelinformation.

In addition, the receiving channel power can be compensated by using theamount of channel power. This can be expressed as shown in Equation 3.

| H _(n)|² =|H _(n)|²+|Ξ_(n)|²  [Equation 3]

Here, |H_(n)|² denotes a receiving channel power of the nth subcarrier,and | H _(n)|² denotes a channel power value compensated by the amountof channel power change according to the user's mobility.

As another embodiment of the present invention, the aforementionedscheme or equations of above can be applied in situations where theuser's mobility is high (or fast).

FIG. 9 is an exemplary structural diagram illustrating a transmittingend and a receiving end using a SCW scheme. FIG. 10 is an exemplarystructural diagram illustrating a transmitting end and a receiving endusing a MCW scheme. The fundamental structures of the transmitting endsand the receiving ends of FIGS. 9 and 10 are the same as those of FIGS.1 and 2. However, the difference is that in the receiving 200 of FIGS. 9and 10, the receiving channel power can be measured in terms of per eachsubcarrier or per subcarrier group. In addition, an index selectionmodule 210 is added for generating the feedback information based on anindex having large fading and an index that can be compensated and usedfor retransmission.

More specifically, the index selection module 210 can include areceiving channel measurement unit (not shown) configured to measurereceiving channel power of each subcarrier or of each subcarrier groupcorresponding to each transmit antenna. The measured channel power valuecan be compared to a predetermined threshold value, and the subcarrierindex or the subcarrier group index having large fading can be stored.The module can then further include a buffer (not shown) to store thesubcarrier index or the subcarrier group index that are greater than thepredetermined threshold. Lastly, the feedback information can begenerated based on the determination by the index selection module 210and send the generated feedback information to the transmitting end 100.

As for the transmitting end 100, an allocation controller 110 is addedto control the resource allocation module 106′ during retransmission.More specifically, the allocation controller 110 can be configured toreceive the feedback information from the receiving end 200. Duringretransmission, the resource allocation module 106′ can controltransmission by changing the subcarrier index, having large fadingduring initial transmission, with the subcarrier index having goodchannel condition.

The structures as illustrated in FIGS. 9 and 10 are merely examples andas such, the structures can be configured differently.

FIGS. 11 and 12 are exemplary diagrams illustrating comparison ofretransmission methods according to the embodiments of the presentinvention to the conventional retransmission methods.

FIG. 11 illustrates the conventional retransmission. More specifically,data is transmitted via two transmit antennas (e.g., Tx1 and Tx2). Ifthe subcarrier bandwidth experiencing large fading are the same(illustrated in dotted circles) for each transmit antenna, there is nocompensation for data loss except for the possible gain achieved byretransmission itself, even when the retransmission are made viadifferent antenna or by a fixed antenna.

However, FIG. 12 illustrates retransmission of data according to atleast one of the embodiments of the present invention. Here, theretransmission is made by changing or reassigning the subcarrierbandwidth. More specifically, the data assigned to the subcarrierbandwidth which experienced large fading during initial transmission isreassigned to the subcarrier bandwidth having good channels so that thedata can be retransmitted under more favorable and reliable conditions.As illustrated in FIG. 12, with this arrangement, retransmission cancompensate for poor initial channel condition and thus, provides morereliable retransmission.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of transmitting data in a wireless communication system, themethod comprising: receiving a first group index and a second groupindex, wherein the first group index represents indices of a grouphaving channel power below a specified threshold value and the secondindex group index represents indices of a group having channel powergreater than or equal to the specified threshold value; and transmittingthe data after swapping mapping locations of the first group index andthe second group index.
 2. The method of claim 1, wherein the thresholdvalue is configured based on level of fading.
 3. The method of claim 1,wherein the data is transmitted via a different antenna after theswapping.
 4. The method of claim 3, wherein the group includes at leastone subcarrier, and a number of subcarriers in the group corresponds toa correlation value of each subcarrier.
 5. The method of claim 1,further comprising: measuring the channel power of a receiving channelin terms of subcarriers or subcarrier groups per each antenna; andgenerating feedback information based on the measured channel power. 6.The method of claim 1, wherein the first group index and the secondgroup index are stored in form of arrays.
 7. The method of claim 1,wherein a number of the first group index and a number of the secondgroup index independently correspond to the subcarrier index grouphaving channel power less than or greater than or equal to a certainthreshold.
 8. A method of retransmitting data in a wirelesscommunication system, the method comprising: measuring power values of areceiving channel in terms of subcarriers or subcarrier groups per eachantenna; generating feedback information based on the measured powervalues; receiving the feedback information regarding channel informationin terms of the subcarriers or the subcarrier groups for each transmitantenna; allocating the data to the subcarriers or the subcarriergroups, which were mapped to the subcarriers or the subcarriers groupshaving relative poor channel condition, to the subcarriers or thesubcarrier groups having relative good channel condition; andretransmitting the data on the allocated subcarriers or the subcarriergroups via a plurality of antennas.
 9. The method of claim 8, furthercomprising determining index of subcarriers experiencing large fading bycomparing the measured power values with a specified threshold value.10. The method of claim 8, wherein the specified threshold value isdetermined based on severity of fading.
 11. The method of claim 8,wherein the transmit antennas are fixed for retransmission.
 12. Themethod of claim 8, wherein the subcarrier group comprises at least onesubcarrier.
 13. The method of claim 8, wherein the power valueassociated with each subcarrier group represents an average power of thesubcarriers in each group.
 14. The method of claim 8, wherein the powervalues are change in correspondence with amount of movement by thereceiver.
 15. The method of claim 14, wherein if the amount of movementby the receiver is high, the power values are compensated by|Ξ_(n)|²=(1−|ρ|²)σ_(h) ² where |Ξ_(n)|² denotes the amount of change inchannel power according to the receiver's mobility, σ_(h) ² denotesaverage energy of the channel, and ρ denotes a variable acquired byusing Bessel function with respect to Doppler frequency and time delayin time-varying channel environment.
 16. The method of claim 15, whereinρ is further expressed byρ=J ₀(2πf _(d)τ_(d)) where J₀(•) denotes Bessel function, f_(d) denotesDoppler frequency, and τ_(d) denotes time delay, and ρ is inverselyproportional to user's mobility in that ρ decreases with increase in thereceiver's mobility, and conversely, ρ increases with decrease inreceiver's mobility.
 17. The method of claim 14, wherein the powervalues are compensated by| H _(n)|² =|H _(n)|²+|Ξ_(n)|² where |H_(n)|² denotes a receivingchannel power of the nth subcarrier, and | H _(n)|² denotes a channelpower value compensated by the amount of power change according to thereceiver's mobility.
 18. An apparatus for retransmitting data in awireless communication system, the apparatus comprising: at least oneencoder configured to attach error correction bits; at least one hybridautomatic request function module configured to perform at least one ofretransmission and rate matching; at least one mapper configured toconvert parallel signals into symbols; a resource allocation moduleconfigured to allocate the data to subcarriers; and an allocationcontroller configured to receive feedback information from a receiver,wherein the resource allocation module controls transmission by changingthe subcarrier index, having large fading during initial transmission,with the subcarrier index having good channel condition.
 19. Anapparatus for retransmitting data in a wireless communication system,the apparatus comprising: at least one fast Fourier transform (FFT)module configured to process the symbols transmitted from a transmitter;at least one demapper configured to convert the symbols into signals; anindex selection module configured to measure receiving channel power ofeach subcarrier or each subcarrier group corresponding to each transmitantenna; and a storage unit configured to store at least one subcarrierindex or at least one subcarrier group index, wherein the measuredchannel power is compared to a predetermined threshold value and thesubcarrier index or the subcarrier group index whose value I is greaterthan or equal to the predetermined threshold value is stored in thestorage unit.
 20. The apparatus of claim 19, further comprising:generating feedback information based on the measurement from the indexselection module; and transmitting the feedback information to thetransmitter.